BXH-2 mice develop a high incidence of myeloid leukemia that is causally associated with the expression of an ecotropic murine leukemia virus (MuLV). The MuLVs are acting as insertional mutagens to alter at the expression of cellular protooncogenes that contribute to leukemia. Since myeloid leukemia is rare in mice and 100% of BXH-2 mice develop this leukemia, BXH-2 mice represent a unique and powerful model system for the identification of genes involved in myeloid leukemogenesis. We have demonstrated that the analysis of the viral integration sites identifies new loci (Evi2) involved in human as well as murine disease. However, we have shown that integrations into Evi2 are present in only 10% of the tumors analyzed, indicating that there exists several other loci that are targets from viral integration and participation in myeloid tumorigenesis. We have recently identified a nw common site of integration, Meis1 (Myeloid ecotropic viral integration site 1), in the BXH-2 myeloid tumors. We have found that 15% of the tumors have viral integrations within Meis1 and that the chromosomal location of Meis1 suggests it represents a novel locus. A gene was identified that is flanked by the viral integrations and sequence analysis reveals the gene to be a novel homeobox gene related to the PBX homeodomain family (one member which is involved in pre-B cell lymphomas). Our goals in this proposal are to characterize the role of Meis1 in development and leukemia. In addition, we plan to identify additional common sites of viral integration in the BXH-2 tumors as well as begin to identify the role of the host BXH-2 mice in developing myeloid leukemia. These results will provide information not only as to types of genes that contribute to leukemia, but also to the genes that are involved in normal hematopoiesis. The specific goals of this project are to complete the cloning and characterization of the Meis1 genomic locus and its encoded gene. To express the Meis 1 protein in a bacterial expression vector and generate polyclonal antisera against at the Meis1 protein. The antisera will be used to confirm the nuclear localization of Meis 1 as well as study the developmental expression. The bacterially generated fusion protein will be used to begin to identify the binding site of Meis1. The role of Meis1 in myeloid cell development and leukemia will be explored by the overexpression of sense and antisense transcripts in myeloid cell lines and murine bone marrow. The results of these three aims will enhance our understanding of the function and expression of a novel homeobox containing gene. In addition, we plan to isolate additional common site of viral integration, with the aim of identifying complementation groups of integration sites. Finally, we are going to explore the mechanics of the myeloid cell compartment in BXH-2 mice to determine what role the host has in conferring the disease specificity. The results obtained in this project will build on the existing database of genes involved in murine myeloid leukemogenesis and the potential role of these genes in human neoplasia. Finally, these studies will provide information as tot the role the host plays in conferring disease specificity.